This invention relates to a process for the isomerization of a halogenated toluene.
The halogenated toluene as referred to herein is a compound resulting from substitution of one hydrogen atom attached to the toluene nucleus by a halogen atom, and it is o-, m- or p-halotoluene.
In general, a halogenated toluene is obtained by a nuclear substitution reaction of toluene with halogen. This halogenation reaction is a strongly o,p-orienting reaction, so that in case it is desired to obtain m-isomer, it is necessary to isomerize o- or p-isomer. The ratio of demand for the halotoluene isomers is in many cases different from their production ratio at the time of halogenation. Therefore, in order to utilize halogenated toluenes effectively, the isomerization process has an important technical meaning.
As conventional examples of such an isomerization reaction there have been known the method disclosed in Olah, G. A., "J. Org. Che." 27, 3464 (1962) which uses aluminum chloride etc. as a catalyst and the method disclosed in Japanese Patent Publication No. 11809/71 which uses HF-BF.sub.3 as a catalyst. However, these conventional methods for the isomerization reaction involve problems such that the catalyst activity is not sufficient and a long reaction time or a large amount of catalyst is needed, and further that the reaction vessel is corroded and it is difficult to separate the reaction product from catalyst components. Thus, none of them have been desirable as industrial isomerization methods.